1. Field of the Invention
The present invention generally relates to control systems used in manufacturing plants, and more specifically to a method and apparatus for implementing an integrated control system to control addressable remote devices used in such plants.
2. Related Art
Control systems generally coordinate and control the operation of various remote devices (also referred to as field instruments) to implement a desired process in environments such as manufacturing plants. Each device in turn contains components such as sensors (which measure various variables such as temperature, flow, pressure, etc.), control elements (e.g., valves, switches), and transmitters (which transmit any desired information).
The decision to operate various control elements is often based on the state (or status) of several variables (e.g., temperature, flow, pressure) in devices implementing a manufacturing process. Accordingly, sensors are generally implemented to monitor the states of interest and send the monitored information to a controller block. For example, a pressure transmitter measures pressure, a flow transmitter measures density and flow between two different positions and sends signals representing the measured parameters using a transmitter. The controller block may send control signals to the control elements (in the devices) based on the measured parameters to implement a desired manufacturing process.
Remote devices are often implemented to be addressable, i.e., an address is provided which identifies a corresponding device. Such an address is often used by systems such as asset management systems to send commands (directed to a specific device) and receive corresponding information. As is well known, an asset management system generally maintains various status related information (such as the device name, type, number of times the device has been used, the different states (e.g., temperature, pressure the device has been subjected to, etc.), and such status information is used for various operation management tasks such as scheduling maintenance.
Multiplexers are often used to enable all such communications between devices and asset management system. In general, a multiplexer forwards a command received from asset management system to one of the devices (as determined by an address in the command), and similarly forwards responses received from corresponding devices to the asset management system.
In an embodiment, multiplexers are implemented substantially in the form of hardware. In general, hardware based approaches do not provide for easy implementation of new features. For example, addition of a new feature in hardware-based implementations may require addition of new modules, which typically requires a lot more effort/cost than in software-based implementations.
Further more, hardware implementations are relatively expensive and also consume additional space. The cost and space requirements are compounded due to the use of multiple units for multiplexers, controller blocks, asset management systems, etc. Accordingly, what is needed is a method and apparatus which provides greater flexibility to add new features and/or minimize space/cost requirements.